Saturday, August 12, 2006

Geared Fan Update: Pratt Steps Up To the Plate.

There's an interesting article in the Seattle Times about Pratt making a pitch to place its geared fan engine on whatever replaces the B737. I blogged about this very subject back in April, and the link to the Flight International article on the Pratt multi bajillion dollar effort to take geared fan technology and apply it to large engines is most informative.

As the price of oil spirals on upward, anything that promises a substantial fuel economy increase and a noise decrease will come with a built in set of selling points that the airframe people will find hard to resist, especially if the pressure's coming from the operator community.

The Times suggests that this could be a roll the dice, bet the limit, last chance at the brass ring opportunity for Pratt to regain its place in the commercial engine field that it lost when the CFM56 came along because it was doing so well with the JT8. Steve Heath, leading up the charge for Pratt, seems to be in agreement.

The interesting thing is that this is the same sort of blinkered philosophy that allowed Pratt to clean Curtiss Wright's clock. One day in 1948, C-W announced to all and sundry that it wasn't going to spend any money developing turbine engines for commercial applications because they were just plain inefficient, and they had these lovely R3350 Turbo Compounds that had a SFC of about 0.36, which is as good as it gets. My father was there and he, along with half the engineers in the place, took off for other places-one of which was Pratt and Whitney, who knew better.

One thing I can tell Steve is that it's a lot harder than it looks, but I am sure he knows that.

Honeywell, which used to be GTEC, developed the TFE731 starting in the sixties, and it too has a planetary fan reduction gear. When I went to work for Garrett in the early eighties, we were still doing service bulletins to extend the life of the planetary gearset, and it was around that time that they gearboxes started being bulletproof. It took Garrett twenty years and a lot of money to get to that point.

Likewise, Avco Lycoming thought it could put together a cheap geared fan engine in the ALF502, which almost took down Avco Lycoming, British Aerospace, and Canadair all in one fell swoop because it ain't as easy as it sounds.

The problems that bedeviled the Garrett fan gearbox were many and varied, but they stuck with it, spent the money, and came out of it with a fine engine that is quiet, efficient and reliable in the field. In fact, as I recall, one of the last things we were doing was installing a special spring washer in a groove on the sun gear to change the resonant frequency of said gear back in the early eighties. I still have the special tool, by the way.

So my hat's off to Pratt, because they're daring greatly. This is uncharted territory for anyone. Let us fervently hope it is a howling success.


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